SANTA CLARITA, CALIF.
— They are two of the largest housing developments in the history of the American West. They may be, because of dwindling open space, the last two projects of their size (60,000 and 70,000 residents) in California.

Slated for construction alongside the state's most important north-south artery, the already traffic-choked Golden State Freeway (I-5), are causing the most heated debate in years over the quality of life here and the Pandora's box of issues that surround it: population increase, immigration, environmental protection, air quality, job creation.

To boosters, the initiatives represent a new kind of housing development - one with elegant greenbelts, local jobs to prevent commutes, and a "village" ethos. But critics see it as just another form of sprawl, tarted up with nice labels, that will further transform southern California into the world's biggest stucco-scape.

"California is battling with the American ideal of whether or not every family can have its dream of a house with a yard, and if so at what cost to the environment," says Bill Hudnut, senior fellow for public policy at the Urban Land Institute in Washington D.C.

Given the pressures for housing across the country - 18 million more units in California alone by 2025 - experts say the state is learning the hard way how to cope. "People are against sprawl and density," says Mr. Hudnut. "They want natural vistas and jobs near where they live. California is trying to do both and is colliding with its own passionate and contrary points of view."

Exhibit A is Newhall Ranch, which after a decade of controversy was given the green light this month by the Los Angeles County Board of Supervisors, as the county's largest-ever subdivision (20,885 homes). Planned on chaparral-covered rolling hills stretching from the I-5 to the Ventura County line, the 12,000-acre project will add an estimated 60,000 residents, with construction beginning in 2006.

Caught in a classic fight between developers who want to provide homes and environmentalists who want to retain open space, Newhall Ranch is presenting itself as an enlightened compromise. It is a planned community organized around five village "nodes" to provide shopping, schools, industrial parks, and green belts. Over half of the project (6,100 acres) is being retained as open space.

"We had the choice or rushing in helter-skelter or master-planning for the long term, and we chose the latter," says Newhall Land and Farming Co. spokeswoman Marlee Lauffer. The site will mimic the development of the town of Valencia, just miles away, which has 48,000 residents and claims to have created roughly the same number of jobs over the past two decades. "We have built in a permanent funding mechanism so homebuyers will pay for the maintenance of open space, and are creating business opportunities so that the residents will not add to severe traffic problems commuting into Los Angeles," says Ms. Lauffer.

Old sprawl in new clothing

Critics say such motives are laudable in theory and laughable in practice. "In spite of county officials who are trying to make this look like another project that has some semblance of 'new urbanism' and mixed use, this is pretty much just the same sprawl that has been going on in California for a long time and is wrecking the state," says Ron Bottorff, chair of Friends of the Santa Clara River.

He decries the "urban edge effects" produced by paving over landscape, increasing runoff, introducing pets and plants. He says the project will reinforce the river's banks in some areas, which speeds the water flow and stirs up silt, altering habitats of endangered species such as the unarmored threespine stickleback fish. "This is turning one of the last great open spaces near the California coast into a human-affected rather than natural area," he says.

Another major concern is traffic in a Southern California car culture that is notoriously short on public transportation. The two major freeways connecting to Los Angeles just south of Newhall (I 405 and US 101) are already two of the most heavily used corridors in the world.

Related to that is how much local employment can be generated. Planners estimate that only 10 percent of residents will have to leave the area for work, but one county supervisor, Zev Yaroslavsky, says that is "laughable."

Environmentalists, too, find that assertion dubious. They say they heard similar contentions when the so-called Inland Empire of San Bernardino and Riverside, 40 miles east of Los Angeles, was being heavily developed. The much-chronicled story there over the past decade has been the influx of residents pouring in for cheaper homes, but who are also clogging freeways to work in Orange County to the south.

"California developers are building further and further out, creating longer and longer commutes because they are not providing enough jobs in these areas," says Bill Corcoran, regional director of the Sierra Club. He laments a recent proposal to tunnel under the Cleveland National Forest to relieve congestion in the San Bernardino/Orange County corridor.

"We sink billions into new housing infrastructure without thinking of the fundamental problems of where these people are going to work and how they will get there," Corcoran says. "Then we come up with ridiculous and bizarre solutions that remind me of the guys who wanted to blow the smog out of L.A. by using giant fans."

An overnight city

Exhibit B is Tejon Ranch, just 40 miles north of Newhall. It is a development of 23,000 homes slated to begin building in 2007, but not yet formally approved. Developers there also intend well-planned shopping centers, industrial parks, schools, and libraries. And between Tejon and Newhall, which would provide bookends to several smaller subdivisions, another 70,000 residents are expected by 2030, according to the Los Angeles County Department of Public Works.

For all the polemics over the developments, some analysts take a more moderate view. They say that for all their weaknesses, the larger planned communities do, at least, try to consider the longer-term perspective and avoid even worse problems generated by hosts of smaller developments that do not, or cannot, consider regional perspectives.

"No one wants to see the last great open spaces of the state and country disappear under a carpet of development," says Carol Whiteside, of Great Valley Center, a private nonpartisan group that tries to unite diverse interests for sustainable growth. "For all their perceived faults, these developments are trying to come up a coherent, regional, and long-term plans that integrate the concerns of all sides. The alternative is piecemeal development that doesn't fit together at all and can make people more frustrated than they are now."

Observers say the California example is reflective of similar disputes in Phoenix, Albuquerque, Las Vegas, and Florida, which has built to the edge of the Everglades. In search of cheaper homes, buyers create the demand that helps consume open land, often luring businesses and residents from already struggling inner-cities and suburbs. What's often lacking, they say, are forums that bring people together with divergent viewpoints to resolve issues dispassionately.